The present invention relates to a method for reducing the latency time for interactive data communication between a client computer and a server computer connected via a satellite network containing a geostationary satellite, as well as a satellite network for undertaking such a method.
Data communication via satellite networks employs preferably geostationary satellites positioned at a distance of approximately 36 000 km above the surface of the Earth and moving in conjunction with the Earth while maintaining an essentially fixed position in relation to the surface. As a result, when observed from the Earth it appears as if the satellite remains stationary above the area of the Earth's surface which is situated below the satellite and within which communication with the satellite is possible. This area is often referred to as the “footprint”.
This has produced to date a number of satellites lined up practically like pearls on a string at a distance of approximately 36 000 km above the equator.
Because of this great distance and the finite propagation speed of electromagnetic signals, data communication via geostationary satellites is a problem, in that the delay of electromagnetic signals from a transmitter on the Earth to the satellite and from there to the receiver is about 0.24 seconds, so that an answer sent by the receiver without any time delay will not reach the transmitter until approximately 2 seconds later at the earliest due to additional electronic loss of time during signal conversion.
For interactive data communication between a client computer and a server computer, where the server computer undertakes the actual data processing and the client computer simply assumes the function of an intelligent terminal producing for the user of the client computer an interactive screen display using the data transferred by the server computer via the geostationary satellite, this compulsory time delay, also often described as latency time, means that a character entered by the user of the client computer, for example, via a keyboard or a movement of the mouse, is acknowledged on the screen of the client computer by a corresponding echo from the server computer after two seconds at the earliest.
Because this time delay of approximately 2 seconds, which occurs for each user input via the keyboard, mouse or other data input device of the client computer, is unacceptable for interactive data communication, interactive client-server applications such as ASP software with data-driven applications, which are of benefit, for example, in terrestrial connections with a large number of users and can be undertaken with the aid of operating systems like UNIX or Windows 2000 Server etc., are not practicable via geostationary satellites.
On the other hand, satellite connections are best suited to transferring mass data, for example, analogue and digital television programs, videos and Internet downloads, due to their high bandwidth and secure transfer properties and based on the fact that these do not require any interactive inquiries and acknowledgements to be transmitted via the satellites.
These mass data are sent to the geostationary satellite as a continuous data stream via so-called satellite HUBS and central server computers connected to them and distributed by the satellite to a number of satellite receiver stations within the area of the footprint.